During recent years, particularly since the railroads initiated the widespread transportation of semi-trailers on open railroad cars, thievery from trucks has increased at an alarming rate. Not only are loaded trucks, semi-trailers, and containerized units burglarized frequently when left unattended in freight yards, truck terminals and similar commercial and industrial areas, but goods and products are taken from semi-trailers even as they are being pulled through congested areas with slow moving traffic or transported on moving railroad cars.
In most cases, the process of breaking into a truck is relatively simple and requires only a minimum of time. Normally, the loading doors on trucks are at the back end of the truck body where they cannot be viewed by the driver or by someone glancing down a row of railroad cars loaded with semi-trailers. Thus, semi-trailers particularly are vulnerable as targets for thieves.
The closure mechanism for a truck loading door generally is located on the exterior of the truck body and involves a simple cam arrangement which is manually operated and which is "sealed" or locked by a padlock intended to prevent unauthorized actuation of the closure mechanism. Unfortunately, such arrangements can be easily and quickly breached or forced by someone equipped with appropriate knowledge and a bolt cutter or other means for cutting the padlock link. Breaking into a truck can be so quick and simple, in fact, that as pointed out above, it has been known to occur in the middle of slowly moving start/stop city traffic, on slowly moving trains in large railroad yards, and even between cities on country trackage.
Over the years, various suggestions have been proposed for locking devices intended to improve security of the loading doors of trucks and semi-trailers. For example, U.S. Pat. No. 3,624,761 discloses a pneumatically operated system in which a lock assembly is mounted under the floor of a truck. This system includes a locking pin mounted on a bracket extending downwardly from one of the loading doors and adapted to engage a spring mounted latch located under the truck bed as the door is closed. The doors may then be opened upon application of air pressure to an externally mounted pneumatic cylinder to disengage the latch from the locking pin. Another system is disclosed in U.S. Pat. No. 3,045,775 wherein a complex system of hydraulic values and controls is intended to secure inner doors of a vehicle if its exterior doors are breached. Other systems for locking doors of vehicles are described in U.S. Pat. Nos. 2,198,862 and 1,154,439 wherein a latch is maintained in a locking position during such time as pneumatic or fluid pressure or vacuum is maintained in an operating cylinder.
As far as is known, however, none of the prior proposals for securing truck loading doors has met with any significant degree of commercial success. Devices such as those shown in the above mentioned patents are too complicated, expensive, cumbersome, or susceptible of malfunction or tampering to have gained wide acceptance and usage. For example, the externally mounted system in U.S. Pat. No. 3,624,761 not only involves exposure to damaging natural elements (i.e. rainwater, mud, ice accumulation, etc.), but is vulnerable to tampering by a potential thief. The systems in the other three cited patents are such that they require a source of continuous fluid or pneumatic pressure or vacuum to remain effective. Thus, they would be ineffective is separated from such a source.
Accordingly, while others in the art have recognized and attempted to develop systems for preventing the unauthorized opening of truck loading doors, such prior attempts have failed to provide a safe, effective, inexpensive and simple locking system capable of meeting the security needs of today's transportation industry.